Process for making a polyisocyanate-impregnated,paper-overlaid panel

ABSTRACT

AN ORGANIC OLYISOCYANATE SERVES AS BOTH THE IMPREGNANT AND THE ADHESIVE FOR PAPER-OVERLAID PANELS. SUCH PANELS CAN BE USED FOR INDOOR AND OUTDOOR APPLICATIONS AND ESPECIALLY FOR MAKING CONCRETE FORMS. THE POLYISOCYANATES USED HAVE A LOW MOLECULAR WEIGHT AND CAN BY USED WITH OR WITHOUT CATALYSTS AND IN SOLUTION WITH AN INERT SOLVENT. THE PROPERTIES OF THE POLYISOCYANATES USED MAKE IT POSSIBLE TO COMBINE IMPREGNATION AND LAMINATION OF THE OVERLAY PAPER IN ONE STEP AS LONG AS SUBSTANTIALLY CLOSED CONDITIONS ARE USED. THE POLYISOCYANATE REACTING WITH WATER IN THE PAPER AND SUBSTRATE (ESPECIALLY WHEN WOOD) FORMS CARBON DIOXIDE, THE PRESSURE OF WHICH WHEN CONFINED BY THE PRESS WILL FORCE AND DISTRIBUTE THE POLYISOCYANATE INTO THE SUBSTRATE AND PAPER. WHERE THE SUBSTRATE TO BE OVERLAID IS PLYWOOD, THE SAME MAY BE FORMED AT THE SAME TIME AS THE OVERLAY IS PLACED. THE OVERLAY PAPER MAY BE KRAFTR PAPER OF ANY GRADE.

y 1972 HONG MAN LEE 3,666,593

PROCESS FOR MAKING A POLYISOCYANATE-IMPREGNATED, PAPER-OVERLAID PANEL Filed 001'.- 27, 1969 FIG. I.

ATTORNEY.

United States Patent Office U.S. Cl. 156285 14 Claims ABSTRACT OF THE DISCLOSURE An organic polyisocyanate serves as both the impregnant and the adhesive for paper-overlaid panels. Such panels can be used for indoor and outdoor applications and especially for making concrete forms. The polyisocyanates used have a low molecular weight and can be used with or without catalysts and in solution with an inert solvent. The properties of the polyisocyanates used make it possible to combine impregnation and lamination of the overlay paper in one step as long as substantially closed conditions are used. The polyisocyanate reacting with water in the paper and substrate (especially when wood) forms carbon dioxide, the pressure of which when confined by the press will force and distribute the polyisocyanate into the substrate and paper.

Where the substrate to be overlaid is plywood, the same may be formed at the same time as the overlay is placed. The overlay paper may be kraft paper of any grade.

This invention relates generally to a new process for making paper-overlaid panels and to panels made by this process. I

Prior art processes for making paper-overlaid panels, in particular wood panels, suffer from several disadvantages which either limit the applications of the panels thus produced or increase their cost price. For example, such processes require utilization of a specially made paper web for the overlay. Again, in the conventional method of making paper-overlaid panels, impregnation of the resin into the paper and lamination of the impregnated paper onto a substrate are done in two steps. Nevertheless, the impregnant exists only in the overlay. Finally, in laminating a conventional medium density overlay paper onto a substrate, an adhesive must be used.

With a view to departing from the above outlined disadvantages of prior art, the main object of this invention is to provide a novel process for making paper-overlaid panels in which the steps of imprengation and lamination are combined.

An equally important object of this invention is to provide a novel process in which commercially available kraft paper can be used.

Another object of the invention is to provide a novel process for making paper-overlaid panels wherein the impregnant resin penetrates into the wood substrate.

An additional object of the invention is to provide con crete forms made of panels made in accord with the invention which will be alkali-resistant and which can be reused many times.

The foregoing objects and other features and advantages of the invention will be more fully realized as the description thereof proceeds, particularly when taken together with the accompanying drawing wherein:

FIGS. 1-4 are cross-sectional views of paper-overlaid panels made in accord with the invention.

- Referring to FIG. 1, denotes generally a panel, 12 is a substrate which may be wood, plywood, particle board, hardboard, aluminum, steel, asbestos board, plastics, and the like. The overlay 14 can be commercially available kraft paper of any grade. A coating of resin 16 Patented May 30, 1972 impregnates the paper and makes it adhere to the substrate.

The resins used in the practise of the invention are those organic (aliphatic, aromatic or aryl aliphatic) isocyanates having an average functionality of two or more isocyanate (NCO) groups per molecule.

Some examples are:

(1) 4, -diphenylmethane diisocyanate (2) 4,4',4"-triphenylmethane triisocyanate (3) 2,4-tolylene diisocyanate (4) 2,6-tolylenediisocyanate (5 1,fi-hexamethylenediisocyanate (6) 1,5-naphthalenediisocyanate (7) 3,3'-dimethyl-4,4'-'biphenylenediisocyanate(tolidine diisocyanate) (8) 3,3'-dimethoxy-4,4-biphenylene diisocyanate (dianisidine diisocyanate) (9) 3,3-di-methyl-4,4'-diphenylmethane diisocyanate (l0) m-Phenylene diisocyanate (1 1) p-Phenylene diisocyanate (12) 4,4'-biphenylene diisocyanate (xenylene diisocyanate) (13) 1,3-xylylene diisocyanate (14) 1,4-xylylene diisocyanate l5 2,2',5 ,5 -tetramethyl-4,4'-biphenylenediisocyanate l6) 1-phenoxy-2,4 phenylene diisocyanate (17) l-tert-butyl-2,4-phenylene diisocyanate (18) S-tert-butyl-1,3-xylylene diisocyanate (19) 2,6-dichloro-1,4-phenylene diisocyanate (20) tetrachloro-1,3-phenylene diisocyanate (21) 2,4,6-tribromo-1,3-phenylene diisocyanate (22) 4,6-dichloro-1,3-phenylenediisocyanate ('23 4-chlorol,3-phenylenediisocyanate Preferred compounds are those having an average molecular Weight of about to about 600 and in particular: 4,4-diphenylmethane diisocyanate, 4,4',4"-triphenylmethane triisocyanate, mixtures of 2,4- and 2,6-tolylene diisocyanate and hexamethylene diisocyanate. Among these 4,4'-diphenylmethane diisocyanate is best suited for the purposes of this invention because of its relatively low vapor pressure, low toxicity and low cost. Polyisocyanates are readily synthesized by the phosgenation of the corresponding primary amines or salts of the primary amine in a suitable solvent such as o-dichlorobenzene. They can also be synthesized by the Curtius rearrangement of an acid azide in a neutral solvent, by a Hoffman rearrangement of an acid amide or by the Lossen rearrangement of an hydroxamic acid.

The polyisocyanates may be used With or without a catalyst. Man'y organo-metallic compounds and tertiary amines may be used as a catalyst. Some examples are: the acetylacetonates of aluminum, cadmium, chromium, copper, iron, magnesium, nickel, zirconium; the naphthenates of copper, lead, zinc, cobalt, nickel, manganese, iron; the oleates of lead, tin, potassium, cobalt, iron; the octoate of cobalt, tin, zinc. Also operative are other organo-metallic compounds, such as lead benzoate, so-- dium trichlorophenate, lead 2-ethylhexanoate, cobalt linoresinate, di-n-butyltin diacetate, tributyltin acetate, tributyltin cyanate, di-n-butyltin dichloride, dimethyltin and tertiary amines, such as methylmorpholine, N-ethylmorpholine, dimethylethanolamine, diethylcyclohexylamine, triethylamine, triethylene diamine, N,N-dimethylpiperazine, 1,2,4triethylpiperazine.

The polyisocyanates may be diluted with a solvent. The following solvents may be used, benzene, chlorobenzene, orthodichlorobenzene, nitrobenzene, toluene, xylene, methylene chloride, trichloroethylene, dichloroethane, carbon tetrachloride, dibutyl ether, dioxane, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, butyl acetate, and Cellosolve acetate.

Paper made by the sulfate ('kraft) process, because of its high strength, is most suitable for use as the overlay. Paper made with other processes, such as sulfite, soda and semichemical processes, may also be used. The paper can be bleached or unbleached.

For making concrete forms from panels of this invention, in order to obtain an adequate mechanical strength, it is preferred that the paper have the following minimum thickness and weight:

Thickness: 7 mil Weight: 25 lb./ 1000 sq. ft.

These can be the thickness and weight of one or more than one layer of paper. For other applications, the above figures may be lower.

The preferred moisture content of the paper is in the range of 4-15%.

Lumber, plywood, particle board and hardboard of any hardwood or softwood species may be used as a substrate of the overlaid panel. For concrete form application, the adhesive used for laminating the plywood or for bonding the particle board and hardboard should have exterior durability. Some examples of such adhesive are polyisocyanates, resorcinol formaldehyde, phenol formaldehyde, melamine formaldehyde and polyurethane.

The polyisocyanate may be applied on the paper overlay alone or applied both on the paper and on the substrate surface. Due to its low molecular weight and its good aflinity for cellulose, the polyisocyanate can readily penetrate into the paper. No pressure is needed for impregnation. The polyisoeyanate suitably may be applied by dipping, coating, spraying, brushing or by other methods well known to those skilled in this art.

As shown in FIG. 2, both sides of the substrate can be overlaid. However, when only one layer of paper is used, the resin may be put on side A only, or on side B only, or on both as shown on FIG. 3. FIG. 4 shows the possibilities present when 2 sheets of paper are used. Here the resin may be put on side C only; a combination of any 2 or 3 sides or on all four sides.

Adequate adhesion between the overlay paper and the substrate can be obtained when the paper has a solid resin content of 30%. For concrete form application, however, a resin content of 45% or higher is preferred. There is no advantage in having a resin content of more than 150%.

The polyisocyanate applied on the paper acts both as an impregnant and an adhesive. No other adhesive is required for laminating the paper on to the substrate. The paper can be laminated right after the isocyanate is applied or can be laminated some time later. The storage life of the impregnated paper depends on the kind of isocyanate, type of catalyst, moisture content of the paper and the storage conditions, such as humidity and temperature.

When the substrate used is plywood, lamination of the plywood and lamination of the overlay on to the substrate may be done simultaneously.

In the practise of the process of the invention there is provided a substrate and at least one layer of kraft paper. An organic polyisocyanate is applied to the paper and the paper is pressed against the substrate at a temperature and pressure and for a time suificient to cure the organic polyisocyanate resin.

A pressure range of between about 100 and 350 p.s.i., depending upon the precise nature of the substrate, and in particular its resiliency, will be operative for most systems. When wood is used as the substrate, the preferred range is 125-200 p.s.i.

Depending upon the kind of polyisocy'anate resin, catalyst and solvent used, a curing temperature ranging from about 280-340 F. will be satisfactory. Preferably, the

pressure not only forces some of the resin to penetrate into the surface of a wood or similar substrate but also helps in distributing the resin in the overlay paper. For that reason and to prevent foaming of the resin on the paper surface, the hot press should be closed until curing.

In the particular aspect of the invention where the substrate is a cellulosic material such as wood, there is a strong aflinity between the NCO groups of the polyisocyanates and the OH groups of the cellulose and/or of the monomolecularly absorbed water on the cellulose. This gives a very strong and water resistant bond between the paper overlay and the wood substrate.

The following examples serve to illustrate the invention but do not limit its scope:

EXAMPLES Example 1 There was used as impregnant:

Parts by weight Mondur MR polyisocyanate Zirconium acetylacetonate 1,

1 By Mobay Chemical Company. Viscosity of the impregnant at 75 F. was 255 cps.

A film started to form on the surface of the impregnant after it was standing in 50% relative humidity at 75 for about five hours. This was the result of the reaction between the resin and the moisture in the air. The pot life of the impregnant under this film was over 24 hours.

Overlay paper:

Natural kraft wrapping paper, two layers Weight: 0.02 lb./sq. ft. (double layer) Thickness: 7 mil (double layer) Moisture content: 7.2%

Impregnant applying method: Roll on one side of the paper Amount of material: 0.020 pound solid per square foot overlay Substrate:

formaldehyde gluelines Pressing condition: 7

Temperature=300 F. Pressure= p.s.i. Time=3 min.

Example 2 There was used as impregnant:

Mondur MR polyisocyanate with no catalyst Viscosity: 240 cps. at 75 F.

Overlay paper:

Natural =kraft wrapping paper, two layers Weight: 0.036 lb./sq. ft. (double layer) Thickness: 9 mil (double layer) Moisture content: 7.6%

Impregnant applying method: One second dipping, citcess was doctored off with a doctor bar Amount of material:

0.028 pound solid per square footoverlay The impregnant coated paper was wrapped in a sheet of polyethylene film. Lamination of the paper was done 24 hours later. During this period, the isocyanate partially reacted with the moisture in the paper Substrate and pressing condition: Same as Example 1 -78", 5-ply Douglas fir plywood with phenol Example 3 There was used as impregnant:

Parts Mondur. MR polyisocyanate 100 Methyl ethyl ketone 30 Zirconium acetylacetonate 0.5

Example 4 There was used as impregnant:

' Parts NCO-20 polyisocyanate 100 Toluene 30 Zinc naphthenate (8% in mineral spirits) 1 By Kaiser Aluminum and Chemical Sales, Inc.

Viscosity: 55 cps. at 75 F.

Overlay paper: Same as Example 2 Impregnant applying method: Spray on one side of the Amount of material: 0.020 pound solid per square foot overlay Substrate and pressing condition: Same as Example 3 Example 5 There was used as impregnant:

Parts NCO- polyisocyanate 100 Xylene 10 Cobalt octoate (12% in mineral spirits) 1 1 By Kaiser Aluminum and Chemical Sales, Inc.

There was used as impregnant the same material as in Example 1.

Overlay paper:

Natural kraft wrapping paper, three layers Weight: 0.054 lb./sq. ft. (triple layer) Thickness: 13.5 mil (triple layer) Moisture content: 7.5% Impregnant applying method: Roll on one side of the paper Amount of material: 0.043 pound solid per square foot overlay Substrate: Five plies of Ms" Douglas fir veneer were used as the substrate. Lamination of the substrate and lamination of the overlay were done in one step. The paper impregnant was also used as the adhesive for laminating the substrate. Amount of adhesive applied was about 30 pounds per 100 square feet single glueline. Pressing condition:

Temperature=300 F. Pressure=200 p.s.i. Time=5 min.

Example 7 The following three substrates were used:

(1) 3-ply cedar plywood with phenol formaldehyde glueline (2) /8", 3-ply southern pine plywood with phenol formaldehyde glueline (3) 3-ply redwood plywood with phenol formaldehyde glueline All other variables were the same as Example 1.

Example 8 All samples prepared in Examples 1 to 7 were subjected to the following three tests. Results showed no adhesion or internal bond failure of the overlay.

( l) 72 hours continuous boiling in water (2) 10 cycles of 2-hour boiling in water and 22-hour drying at F.

The samples prepared in Examples 1, 2, 3 and 4 were also subjected to concrete pouring tests. Results indicated the panels could be used as a concrete form for more than 40 applications with the following characteristics:

(1) The overlay color would not be changed by the attack of the concrete alkalis (2) The overlay did not stain the concrete surface (3) The overlay did not show internal bond failure (4) The adhesion between the overlay and the substrates was adequate (5) There was no checking and little telegraphing of the wood grain on the surface (6) The panels required little or no oiling (7) The panels required little or no cleaning after each application (8) The panels showed little surface damage.

As previously stated, the overlaid panel of the invention, whether it has an overlay of high or low resin content, can be used for most interior or exterior applications. It is particularly useful for making concrete forms for the following reason: while conventional phenol c paper overlaid concrete forms turn pink when attacked by alkalies in the concrete and may stain the concrete, the overlay of the invention is not attacked by alkalies so there cannot be a staining problem. In an overlaid wood panel made by the present invention, the polyisocyanate resin penetrates not only through the paper but also in the surface of the wood and bonds the wood fibers firmly together. The resin itself is a good water and water vapor barrier, 'which fact significantly minimizes the rate of absorption and desorption of water and water vapor through the overlaid panel surface. For these two reasons, the extent of dimensional movement of the substrate surface is minimized thereby minimizing the surface telegraphing efiect. The polyisocyanate resin which is present in the overlay, in the glueline and in the immediate substrate surface is tough and hard when properly cured. Such hardness confers enhanced resistance towards the abrasive action of concrete encountered during pouring.

An important advantage of the claimed concrete forms is the low permeability of oil, water and solvents through the surface of the overlaid panels forming the same. Because of this, only a little release agent is needed or good parting. In turn, no concrete hangup will remain on the surface of the form and accordingly it becomes unnecessary to clean the form after each use as is normally the case with the presently used forms. Finally, with the forms of the invention there is no internal bond failure or fiber pulling off even at a low level of resin content because the adhesive bond between the resin and the paper fibers is so strong.

While there has been described in the foregoing preferred modes of carrying out the claimed invention, it will be understood that various changes and modifications thereof can be made by those skilled in the art to which it relates to the extent that such variations incorporate the spirit of the invention, they are included within the purview of the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Process for making a paper-overlaid panel which comprises providing a substrate and at least one layer of kraft paper having a moisture content in the range from about 4% to about applying an organic polyisocyanate resin having a molecular weight in the range from about 150 to 600 to said paper, and pressing said layer of paper against said substrate under closed conditions, whereby the formed carbon dioxide will be entrapedl causing internal pressure to impregnate said resin into said paper and into said substrate, and bond said paper to said substrate.

2. The process according to claim 1 including the step of forming a plywood substrate and laminating the same concurrently with the laminating of said paper onto said substrate.

3. The process according to claim 1 wherein said pressure is maintained for a period of time ranging from about 2 minutes to about 8 minutes.

4. The process according to claim 1 wherein said resin is an aliphatic, aromatic or aryl aliphatic isocyanate having an average of two or more NCO groups per molecule.

5. The process according to claim 1 catalyzed by an organometallic compound or by a tertiary amine.

6. The process according to claim 1 wherein said polyisocyanate is diluted with a solvent.

7. The process according to claim 1 wherein there is applied to said paper from about 30 to about 150% by weight of said resin.

8. Process as set forth in claim 1 wherein said layer of paper is bonded against a substrate of woody fibers at a temperature in the range from about 280 F. to

8 p about 340 F, and at a pressure from about 100 to 350 psi.

9. Process as set forth in claim 8 wherein wherein the bonding temperature is approximately 300 F., and the pressure is approximately 275 p.s.i., and the pressing time approximately 3 /2 minutes.

10. Process as defined by claim 1 wherein said polyisocyanate is 4,4-diphenylmethane diisocyanate.

11. Process as defined by claim 9 wherein said polyiso cyanate is a mixture of 2,4 and 2,6-tolylene diisocyanate and hexamethylene diisocyanate.

12. Process as defined by claim 10 wherein said panel is a concrete form board and said paper has a thickness of about 7 mils and a weight of about 25 lb-./ 1000 sq. ft.

13. Process as defined by claim 1 Wherein'said resin consists of 100 parts of polyisocyanate, 30 parts of methylethylketone and 0.5 part of zirconium acetylacetone and has a viscosity of cps. at F., wherein said paper has a weight of 0.026 lb./sq. it, a thickness of 7 mils and a moisture content of 7.2%.

p.s.i.

14. Process as defined by claim 13 wherein said substrate is a thick, 5 ply Douglas fir plywood panel, and wherein said temperature is about 320 F., said pressure about p.s.i., and the time about 3% minutes.

References Cited UNITED STATES PATENTS 2,43 0,479 11/ 1947 Pratt et a1 161-190 X 2,597,025 5/1952 Orth 161-190 X 3,005,728 10/ 1961 Bridgcforth l6l-'190 X 3,240,618. 3/1966 Hemming 161-190 X 3,468,690 9/ 1969 Hemming 161190 X I ROBERT F. BURNETT, Primary Examiner C. B. COSBY, Assistant Examiner US. Cl. X.R. l56-307; l61190, 331; 260-324, 77.5 NC 

